N. N. Makarova

Synthesis of new stereoregular 2,4,6,8-tetraphenylcyclotetrasiloxanes with mesogenic groups and the influence of spatial isomerism on the phase state of individual isomers and their mixtures

The hydrosilylation of four isomers of tetra(dimethylsiloxy)tetraphenylcyclotetrasiloxane with (4′-cyanobiphenyl-4-yl)undec-10-enoate in the presence of a platinum catalyst afforded four liquid-crystalline stereoisomers of phenylcyclotetrasiloxane with mesogenic cyanobiphenyl groups. The reaction was performed for the first time. The influence of the spatial structure of the stereoisomers of tetraphenylcyclotetrasiloxanes with mesogenic groups on the formation of the liquid-crystalline state by thermooptical, X-ray diffraction, and calorimetric methods. The temperatures and enthalpies of phase transitions were determined, and their reversibility was shown. Differences in both the textures of melts formed on cooling and the phase state and in interplanar distances were found by optical microscopy and X-ray diffraction methods. Based on these data, the spatial structure of the isomers was concluded to affect the phase composition and type of packing in the liquid-crystalline state.

Synthesis of difunctional organooxasilacycloalkanes

Abstract2,8-Dichloro-2,4,4,6,6,8,10,10,12,12-decamethyl-5-carbacyclohexasiloxane, 4,7-dichloro-2,2,4,7-tetramethyl-1,3-dioxa-2,4,7-trisilacyclohepatane, and 4,8-dichloro-2, 2,4,8-tetramethyl-1,3-dioxa-2,4,8-trisilacyclooctane were prepared for the first time by heterofunctional condensation of 1,1,7,7-tetrachloro-1,3,3,5,5,7-hexamethyl-4-carbatetrasiloxane with 1,3-dihydroxy-1,1,3,3-tetramethyldisiloxane, of 2,2,5,5-tetrachloro-2,5-disilahexane with dihydroxydimethylsilane, and of 2,2,6,6-tetrachloro-2,6-disilaheptane with dihydroxydimethylsilane, respectively. Hydrolysis of the resulting compounds afforded the corresponding dihydroxy derivatives, andtrans-isomers of some of these derivatives were isolated in individual form.

Self-Organizing Cyclolinear Organosilicon Polymers in Bulk and on the Surface of Water

Cyclolinear organocarbosiloxane polymers with varying content and location of (CH2)n groups in the monomer unit were synthesized by reactions of heterofunctional polycondensation and polyaddition of difunctional organocyclosiloxanes and organocyclocarbosiloxanes. Their bulk properties were studied by differential scanning calorimetry and X-ray structural analysis. It was shown that on introduction of CH2 groups into the methylcyclohexasiloxane unit, the polymer retains the ability to self-organize with formation of a mesomorphic state in a wide temperature range, while on introduction of (CH2)2 fragments in a cyclotetrasiloxane unit or in a bridge connecting two methylcyclotetra(hexa)siloxane units it does not. Comparison of the X-ray data of dihydroxy derivatives of decamethylcyclohexasiloxane and decamethyl-5-carbocyclohexasiloxane with packing of cyclolinear organosilicon polymers in bulk shows that the polymer inherits the layered type of crystalline structure typical for monomers. Langmuir films of cyclolinear polymethylcarbosiloxanes with different design of monomer units were studied as well. It was revealed that all polymers form monomolecular films at the air/water interface, excluding those having longer hydrophobic fragment than hydrophilic ones. The ability to form multilayers depends on the surroundings of Si atom in the bridge between the cycles.

New stereoregular liquid-crystalline phenylcyclosiloxanes

Representatives of stereoregular phenylcyclotetra(hexa)siloxanes with mesogenic cyanobiphenylyl groups cis-oriented relatively to the siloxane ring have been synthesized for the first time. The ability of the compounds to transit to the liquid-crystalline state was confirmed by the thermooptical, X-ray diffraction, and calorimetric methods. The temperatures and enthalpies of the phase transitions were determined, and their reversibility was shown. The bilayered molecular packing with antiparallel arrangement of molecules is the most probable for the smectic A phase of the cyclosiloxanes studied. Taking into account differences in the optical textures and interlayer distances, we cannot exclude completely the possibility of formation of liquid-crystalline phases of other types.

Dimesogenic liquid crystalline organosiloxanes

Liquid crystalline (LC) organosiloxanes with two terminal cyanobiphenylyl groups attached to a linear or cyclic siloxane center through an aliphatic spacer (CH2)n with i = 10 were synthesized. The ability of compounds to pass into the LC state was confirmed by thermooptical, X-ray diffraction, and calorimetric measurements. The temperatures and the enthalpies of phase transitions were determined. The types of LC structures and the capability of one compound for polymesomorphism to form the chiral SmC* phase without a chiral center in the mesogenic group were established. The temperatures and the enthalpies of the reversible phase transitions, crystal ⇌ SmC ⇌ SmA ⇌ melt and crystal ⇌ SmA ⇌ melt, for linear and cyclic LC organosiloxanes, respectively, were determined. Models of molecular packing in the SmA and SmC* phases were proposed based on X-ray diffraction data. A specific feature of the SmA phases of new LC organosiloxanes is a negative gradient of the temperature dependence of the interlayer spacing.

Design and self-assembling behaviour of comb-like stereoregular cyclolinear methylsiloxane copolymers with chiral lactate groups

ABSTRACT Several new comb-like stereoregular cyclolinear methylsiloxane copolymers exhibiting the self-assembling behaviour have been designed and studied. For the resulting macromolecular materials, the chiral mesogenic unit, namely (S)-(–)-4-[1-ethoxycarbonyl)ethoxycarbonyl]phenyl-4′-[11-tetramethyldisiloxyl)-undecenyloxy)-biphenyl-4′-carboxylate, has been used as a side group to assure the mesomorphic behaviour. The mesomorphic and structural properties were studied by the polarising optical microscopy, differential scanning calorimetry and small-/wide-angle X-ray diffraction techniques. The designed copolymers form the orthogonal smectic A* and the tilted smectic C* phases over relatively broad temperature range, down to room temperatures. The obtained results are discussed in order to contribute to better understanding of the molecular architecture–nano-organisation relationship for a specific type of macromolecular system based on the lactic acid derivatives used as a flexible side groups. Graphical Abstract

Effect of the nature of the substituents on the temperature region of existence of the mesomorphic state in transtactic cyclo-linear polymethyl(phenyl)siloxanes☆

Abstract Transtactic cyclo-linear methyl(phenyl) siloxane polymers and copolymers forming a mesomorphic phase over a wide temperature range have been synthesized. On the basis of data from differential scanning calorimetry and X-ray diffraction analysis, the phase diagrams for different numbers of phenylgroups in the repeating unit are derived and the values of T g and T m are compared with the corresponding values for linear polydimethyl- and polydiphenyl-siloxanes An increase in the number of phenylgroups in the repeating unit is accompanied by an increase in the heat of melting and a decrease of the heat of isotropization.

A Study of the Polycondensation of (Tetrahydroxy)(Tetraaryl)Cyclotetrasiloxanes under Equilibrium and Non-Equilibrium Conditions in the Presence and Absence of Montmorillonite

Oligo- and polycyclosiloxanes were obtained by the polycondensation of (tetrahydroxy)(tetraaryl)cyclotetrasiloxanes in equilibrium and non-equilibrium conditions in the presence and absence of montmorillonite (MMT). Their composition and the structures of their components were investigated by infrared (IR) spectroscopy, 29Si nuclear magnetic resonance (NMR) spectroscopy, atmospheric pressure chemical ionization (APCI) mass spectrometry, powder X-ray diffraction (XRD), and gel-penetrating chromatography (GPC). Also, a comparison of polymers formed in the presence of MMT and via anionic polymerization was performed showing differences in their structures.

Modeling of structures of poly(oxyhexaorganocyclotetrasiloxy-2,6-diyl) mesophases

The idealized liquid-crystal structures of two cyclolinear organosilicon polymers, viz., poly(oxyhexaorganocyclotetrasiloxy-2,6-diyls), where the alkyl substituent is Et (1b) or Pr (1c), were modeled. The columns of monomer units in polymers have different conformations, viz., a distorted long boat in 1b and a distorted long chair in 1c. Both polymers have columnar structures with the most probable antiparallel arrangement of the columns.

Synthesis and some properties of functional linear and cyclic polyethylsiloxanes

Conclusions1.The stepwise condensation of ethylchlorosilane with diethylsilanediol and 1,3-dihy-droxytetraethyldisiloxane was used to obtain 2,6- and 2,8-dichloroethylcyclotetra (penta, hexa) siloxanes. It was established that the reaction is accompanied by intramolecular cyclization in the reaction with 1,3-dihydroxytetraethyldisiloxane: in the first step with the formation of chloropentaethylcyclotrisiloxane and in the second step with the formation of 2,8-dichlorodecaethylcyclohexasiloxane and its structural isomer.2.An increased tendency to form ethylbicyclo [3.5.1]penta- and ethylbicyclo[5.5.1]-hexasiloxane was observed in the hydrolysis of 2,6-dichlorooctaethylcyclopenta- and 2,8-dichlorodecaethylcyclohexasiloxanes.